Tolfenamic acid. Detection and structure of urinary metabolites

N-(2-Methyl-3-chlorophenyl)anthranilic acid (tolfenamic acid) and its metabolites in serum and urine were analyzed by a reversed-phase ion-pair HPLC method. The major metabolites were N-(2-methyl-3-chloro-4-hydroxyphenyl)anthranilic acid, and one of the minor metabolites was N-(2-formyl-3-chlorophenyl)anthranilic acid, i.e., products resulting from hydroxylation in either the methyl group or the methylchlorophenyl group of tolfenamic acid, and further oxidation of the hydroxymethyl group to a formyl group.